Can use of decadron 4 mg /day by a 70 yrs old liver cancer patient cause severe fatigue?

It depends: Steroids are commonly used to treat chronic fatigue and are proven useful in the short terms. But the use of a potent steroid like Decadron for more than 1-2 months can cause muscle weakness(Myopathy) which often affects the proximal muscles like the Quadriceps, making it difficult to get up from a sitting position. Dose reduction to 2 mg/day will benefit this patient.